The Effects of Thermal Gradients in Automotive Battery Packs - - PowerPoint PPT Presentation

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The Effects of Thermal Gradients in Automotive Battery Packs - - PowerPoint PPT Presentation

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The Effects of Thermal Gradients in Automotive Battery Packs Balancing Strategy Dr Alastair Hales Mechanical Engineering Imperial College London Thermal Performance of Lithium-Ion Batteries Temperature effects Thermal gradients in

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SLIDE 1

The Effects of Thermal Gradients in Automotive Battery Packs Balancing Strategy

Dr Alastair Hales Mechanical Engineering Imperial College London

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SLIDE 2

Thermal Performance of Lithium-Ion Batteries

Temperature effects in your battery Modelling thermal gradients Thermal gradients in your pack Battery thermal performance Thermal gradients in your battery The Cell Cooling Coefficient Thermal management methods Application and innovation

50 100 150 200
  • 50
  • 100
  • 150
  • 200
  • 13 °C
  • 5 °C
5 °C 15 °C 25 °C 35 °C 45 °C 55 °C
  • Zimag [m]
Zreal [m] Decreasing temperature 0.1 Hz 1 Hz 10 Hz 3 6 9 12 15
  • 3
  • 6
  • 9

𝑫𝑫𝑫𝒋 = ൘ ሶ 𝑹𝒋 ∆𝑼𝒋

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SLIDE 3

How does temperature affect your battery?

  • Temperature affects impedance

exponentially

  • Non-linear temperature dependence on charge
transfer resistance
  • Two common thermal management methods

for pouch cells

  • Surface cooling
  • Tab cooling
  • Thermal gradients within battery packs

are inevitable

50 100 150 200
  • 50
  • 100
  • 150
  • 200
  • 13 °C
  • 5 °C
5 °C 15 °C 25 °C 35 °C 45 °C 55 °C
  • Zimag [m]
Zreal [m] Decreasing temperature 0.1 Hz 1 Hz 10 Hz 3 6 9 12 15
  • 3
  • 6
  • 9
Troxler, Y. et al. Journal of Power Sources, Vol 247, Pages 1018-1025 (2014)
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SLIDE 4

How do thermal gradients affect your pack?

  • Pack-level thermal gradients induce current

inhomogeneities

  • Uneven cell-to-cell loading
  • Suboptimal pack operation
  • Uneven current distribution leads to non-uniform cell

heat generation rates

  • Thermal gradients affect parallel cells at pack-level in

the same way they affect parallel layers at cell-level

Wu, B. et al. Journal of Power Sources, Vol 243, Pages 544-554 (2013)
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SLIDE 5

Are there good and bad thermal gradients?

Tab cooling

  • Some thermal gradient within a layer
  • Very low layer-to-layer thermal gradients
  • Very low layer-to-layer current inhomogeneities
  • Each layer behaves the same
  • Each layer is loaded evenly over a dynamic drive cycle

Surface cooling

  • Low thermal gradients within a layer
  • Significant layer-to-layer thermal gradients
  • Significant layer-to-layer current inhomogeneities
  • Layers behave differently to one another
  • Layers are loaded unevenly over a dynamic drive cycle
Hunt, I. et al. Journal of the Electrochemical Society, Vol 163, Pages A1846-A1852 (2016)
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SLIDE 6

Are there good and bad thermal gradients?

Tab cooling

  • Some thermal gradient within a layer
  • Very low layer-to-layer thermal gradients
  • Very low layer-to-layer current inhomogeneities
  • Each layer behaves the same
  • Each layer is loaded evenly over a dynamic drive cycle

Surface cooling

  • Low thermal gradients within a layer
  • Significant layer-to-layer thermal gradients
  • Significant layer-to-layer current inhomogeneities
  • Layers behave differently to one another
  • Layers are loaded unevenly over a dynamic drive cycle
Hunt, I. et al. Journal of the Electrochemical Society, Vol 163, Pages A1846-A1852 (2016)

Yes

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SLIDE 7

Tab cooling vs. surface cooling

  • Surface cooling causes accelerated

degradation, compared to tab cooling

  • Tab cooling triples the usable life of an EV

battery

Hunt, I. et al. Journal of the Electrochemical Society, Vol 163, Pages A1846-A1852 (2016) Ardani, M. I. I., et al. Energy Vol 144, Pages 81–97 (2018) https://www.youtube.com/watch?v=_jd8REVB-c8
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SLIDE 8

Tab cooling vs. surface cooling: ECM

  • Developed temperature profile
  • ver a 6C discharge
  • Tab cooling, following discharge:
  • 82.5% reduction in temperature
distribution
  • 80% reduction in current distribution
  • 93% reduction in depth of discharge
distribution Zhao, Y. et al. Journal of the Electrochemical Society, Vol 165, Pages A3169-A3178 ∆𝑻𝒑𝑫𝒏𝒃𝒚 = 𝟗. 𝟏𝟏% ∆𝑻𝒑𝑫𝒏𝒃𝒚 = 𝟏. 𝟔𝟕% ∆𝑼𝒏𝒃𝒚 = 𝟗. 𝟏°𝑫

Tab Cooled Surface Cooled

∆𝑼𝒏𝒃𝒚 = 𝟐. 𝟓°𝑫 ∆𝑱𝒏𝒃𝒚 = 𝟏. 𝟕𝑫 ∆𝑱𝒏𝒃𝒚 = 𝟒. 𝟏𝑫 Simulation domain
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SLIDE 9

Why is tab cooling so effective?

Hunt, I. et al. Journal of the Electrochemical Society, Vol 163, Pages A1846-A1852 Zhao, Y. et al. Journal of the Electrochemical Society, Vol 165, Pages A3169-A3178
  • Non-isotropic thermal conductivity

in a cell

  • 𝑽 = Τ
𝒍 𝒚
  • keff for tab cooling is 2 orders of

magnitude greater

Tab Cooled Surface Cooled

ሶ 𝑹 = 𝑽 𝑩 ∆𝑼

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SLIDE 10

Why is tab cooling so effective?

  • LIB A (5Ah Kokam SLPB11543140H5), power cell:
  • LIB B (7.5Ah Kokam SLPB75106100), energy cell:

ሶ 𝑹 = 𝑽 𝑩 ∆𝑼

LIB A LIB B

keff thru-layer (tab cooling) 65.2 W/mK 36.7 W/mK keff layer-to-layer (surface cooling) 0.91 W/mK 0.64 W/mK
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SLIDE 11

Why is tab cooling not universal?

Hales, A. et al. Paper under review
  • Cross-sectional area through which cooling

must occur

  • The tabs are a significant thermal bottleneck
  • Cells are designed for to optimise energy or

power density

  • Surface cooling is ‘easiest’

ሶ 𝑹 = 𝑽 𝑩 ∆𝑼

LIB A LIB B

Area, both tabs 14 mm2 2.78 mm2 Area, single surface 4,520 mm2 9,084 mm2 Which surface would you pick to remove heat from your cell?
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SLIDE 12

How do we improve cell thermal management?

Hales, A. et al. Paper under review
  • Cell redesign to optimise internal

thermal pathways

  • Quantify a cell’s heat rejection

capabilities 1. A metric for cell designers to enhance 2. A standard against which all cells may be compared 3. A tool for battery pack design engineers to use in the initial design stages

Relevant Datasheet Information: LIB A

Capacity (Ah) 5 Energy Density (Wh/kg) 140 Rated Charge Rate (C-Rate) 2 Rated Continuous Discharge Rate (C-Rate) 30 Rated Pulse Discharge Rate (C-Rate) 50

Energy Performance Power Performance

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SLIDE 13

How do we improve cell thermal management?

Hales, A. et al. Paper under review
  • Cell redesign to optimise internal

thermal pathways

  • Quantify a cell’s heat rejection

capabilities 1. A metric for cell designers to enhance 2. A standard against which all cells may be compared 3. A tool for battery pack design engineers to use in the initial design stages

Relevant Datasheet Information: LIB A

Capacity (Ah) 5 Energy Density (Wh/kg) 140 Rated Charge Rate (C-Rate) 2 Rated Continuous Discharge Rate (C-Rate) 30 Rated Pulse Discharge Rate (C-Rate) 50 Cell Cooling Coefficient (W/K) ??

Energy Performance Power Performance

Thermal Performance

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SLIDE 14

Why do you need the Cell Cooling Coefficient?

Hales, A. et al. Paper under review
  • Many cell parameters affect heat rejection
  • Decoupling highly complex and rarely conducted
  • Subsequent knowledge gap
  • Heat rejection from cells is not

quantified

Component Negative CC Positive CC Separator Anode Cathode Casing LIB A k/ W.m-1K-1 398 238 0.34 1.58 1.04 238 Volumetric proportion of cell 9.38% 9.38% 21.42% 33.93% 25.89% 2.75% LIB B k/ W.m-1K-1 398 238 0.33 1.045 0.44 238 Volumetric proportion of cell 4.53% 4.66% 11.72% 45.46% 33.62% 3.77% Parameter LIB A LIB B Cell length/ mm 113.0 89.5 Cell width/ mm 40.0 101.5 Cell thickness/ mm 11.3 7.4 Negative tab width/ mm 20.0 7.0 Negative tab thickness/ mm 0.3 0.2 Positive tab width/ mm 20.0 6.9 Positive tab thickness (cell side of weld)/ mm 0.4 0.2 Positive tab thickness (at weld)/ mm 0.6 0.4 Positive tab thickness (tab side of weld)/ mm 0.2 0.2 Negative tab internal length 13.0 10.0 Positive tab internal length 13.0 10.0 Tab locations (on the cell) Opposite ends Same end Negative Tab Position (width dimension) Central 4.5mm offset Positive Tab Position (width dimension) Central 30.9mm offset Negative Tab Position (Thickness) Central Fully offset Positive Tab Position (Thickness) Central Fully offset

What temperature gradient do you need to remove 1W of heat from your cell?

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SLIDE 15

Cell Cooling Coefficient

Hales, A. et al. Paper under review

1. The rate of heat rejection for a given thermal gradient 2. A constant for a certain cell and thermal management method 3. A standard against which any two cells may be compared

𝑫𝑫𝑫𝒋 = ൘ ሶ 𝑹𝒋 ∆𝑼𝒋

LIB A LIB B CCCtab (W/K) 0.332 0.204

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SLIDE 16

How do you use the Cell Cooling Coefficient?

Hales, A. et al. Paper under review
  • A worked example:
  • A 15Ah battery pack to be designed
  • Must be capable of a 4C discharge
  • Entire pack must be kept below 40oC
  • The ambient air temperature is 20oC
Cell CCCtab (W/K)
  • Max. discharge
C-Rate Capacity (Ah) LIB A 0.332 30 5 LIB B 0.204 5 7.5

Cell Datasheet Information

  • Averaged over a 4C discharge:
  • LIB A generates 4.97W of heat
  • LIB B generates 8.28W of heat

∆𝑼𝒅𝒇𝒎𝒎 𝒏𝒃𝒚 𝒖𝒑 𝒖𝒃𝒄𝒕= ሶ 𝑹𝒉𝒇𝒐 𝑫𝑫𝑫𝒖𝒃𝒄

∆TLIB A = 15.0oC ∆TLIB B = 40.6oC

Ttab max = 25.0oC Ttab max = -0.6oC

5oC above ambient 20.6oC below ambient

Down-selection:

  • LIB A is suitable for application
  • LIB B is entirely unsuitable for application,
despite all existing datasheet indicators suggesting otherwise
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SLIDE 17

A thank you to all colleagues at Imperial College London

On this project Dr Laura Bravo Diaz, Mohamed Waseem Marzook, Yan Zhao, Dr Yatish Patel*, Dr Gregory Offer* Other Academics* Dr Monica Marinescu Dr Huizhi Wang Dr Billy Wu Dr Samuel Cooper Prof Nigel Brandon Prof Ricardo Martinez- Botas Other Group Members Dr Karthik Radhakrishnan Dr Ganesh Madabattula Dr Simon O’Kane Dr Shen Li Dr Binbin Chen Dr Chen Zhang Dr Alex Holland Dr Teddy Szemberg O- Connor Dr Abir Ghosh Dr Tribeni Roy Dr Xinhua Liu Dr Weilong Ai Dr Nina Meddings Dr Jingyi Chen Dr Chenzhen Ji Ian Campbell Xiao Hua Emma Vendola Mei-Chin Pang Ryan Prosser Oisin Shaw Max Naylor-Marlow Anna Tomaszewska Khairul Bin Mohammed Natasha Fiig Dr Jacqueline Edge Dr Martina De Marco Nicholas Dean